The invention disclosed and claimed herein generally pertains to the field of apparatus which is capable of detecting mechanical vibrations which are of very low g-level, and which are of such short duration that they may be considered to comprise a pulse of vibrations, or vibrational pulse. More particularly, the invention pertains to apparatus of the above type which employs a very inexpensive sensor element to detect the occurrence of a low g-level vibrational pulse. Even more particularly, the invention pertains to apparatus of the above type wherein a bridge rectifier device, such as a diode bridge, is employed as a transducer element to convert a low g-level vibrational pulse into a usable voltage signal.
It has become known to those of skill in the art that important advantages may be realized by including a timed self-detonating feature in certain types of land mines. By providing such feature, mines which are deployed against an enemy force will be rendered harmless, at a point in time which is known, if they are not first encountered by the enemy. After the known point in time, the mines will not pose a hazard to friendly forces which enter the area of mine deployment. The merit of including a timed self-detonating feature in a mine is shown in the prior art, for example, in U.S. Pat. No. 3,384,017, issued to Lazarus et al. on May 21, 1968, for a "Land Mine Control System".
It has been found that in the development of a time controlled self-detonation system for a land mine, stringent testing procedures may be required to insure that the system reliably activates a mine detonator at the conclusion of a prespecified period. As part of such testing procedures, it may be desirable or necessary to deploy on the order of 100-200 test mines in an operational environment, for example, by air drop. Each test mine would contain a detonator and a timed self-detonating system, but no explosive charge. Following deployment, the time elapsing between deployment and detonator activation would be monitored for each mine. Because of the large number of mines involved in such field test, because of the probable dispersal of the mines over a wide area, and because of the intended time period between deployment and self-detonation, which may be on the order of several weeks, such time monitoring efforts would be most accurately accomplished by dedicating a discrete monitoring device to each test mine, and placing it proximate thereto. However, when the detonator of a mine such as a land mine is activated, the only indication thereof is mechanical vibration which is of very low g-level, and which is of such short time duration that it may be thought of as a vibrational pulse. Consequently, in order to determine the time of operation of a self-detonation system employed by such mines, it is necessary to provide a monitor device which includes a sensory or transducer element which is capable of generating a signal in response to low g-level vibrational pulse.
In the prior art, a device known as a piezoelectric accelerometer is available which may be capable of detecting faint vibrational pulses generated by mine detonation. However, one of such devices may cost on the order of several hundred dollars. If it is necessary to dedicate one monitor device to each mine in a test group of 200 mines, as aforementioned, the total cost of all the monitor devices required for a single field test could become prohibitively expensive. Also, it has been found that such accelerometer devices may be unable to provide sufficient accuracy in timing mine self-detonation.
Certain types of capacitor devices are also available in the prior art which may be capable of detecting low g-level vibrational pulses. However, the signals outputted by such capacitors in response to low g-level pulses may be too weak to be employed in a mine detonation monitor device.
In the present invention, a system is provided for monitoring detonation within a mine such as a land mine, wherein a bridge rectifier is employed to detect a low g-level vibrational pulse, and to provide an output signal in response thereto which is of sufficient strength that it may be employed by the monitoring system to indicate the occurrence of detonation. It has been found that a suitable bridge rectifier may be formed by an interconnection of four diodes, so that the cost of the pulse sensing element of the monitor is negligible, in comparison with the cost of the aforementioned piezoelectric accelerometer. The bridge rectifier of the invention is interconnected with several other solid state components to provide a very inexpensive monitoring system which is capable of enabling an observer to visually determine that mine detonation either is occurring or has occurred, and further enables the observer to readily determine the time that has elapsed between mine deployment and mine self-detonation.